1. Field of the Invention
The invention relates to a ureter resectoscope with an elongate flexible stem tube of substantial length and small external diameter that bears on its distal end an electrode that can be supplied with high-frequency current and on its proximal end is fixed and electrically contacted on a slider mounted so as to be longitudinally displaceable.
2. Description of Related Art
The basic design of generic ureter resectoscopes corresponds to that of the normal urological resectoscope, which is used principally for prostate resection. For this purpose the normal resectoscope only needs to be introduced a short distance through the urethra and thus can have a relatively large diameter with a relatively short stem length.
However, the ureter resectoscope is used in the ureter, that is to say the narrow body channel between the bladder and the kidney. Therefore, it must be substantially longer and thinner than the normal resectoscope. The stem typically has a length of 40 cm and a diameter of at most 3–4 mm. Moreover, the stem must be flexible, since for anatomical reasons it must be greatly bent during introduction.
However, the mode of operation of the ureter resectoscope should correspond as closely as possible to that of the normal resectoscope. Thus, an electrode supplied with high-frequency current with an instrument carrier is moved along in the visual range of the optical unit in order to be able to cut tissue. In this case the usual cutting loop, which cuts as it is retracted against the distal edge of the insulating distal end piece of the stem tube, is used.
For reasons of space in the narrow stem tube, in the ureter resectoscope the rod-shaped instrument carrier is mounted in the same angular position parallel to the optical unit over the entire length of the stem tube. Thus, when the stem tube is bent, the optical unit and the instrument carrier extending parallel thereto are bent at different radii, so the direction of bending is significant. If the instrument carrier lies above the optical unit and is bent laterally, then the bending radii are the same. If the distal end of the stem tube is bent upwards, then the bending radius of the instrument carrier is smaller, so that with the enforced parallel guiding in the stem tube and with the fixed proximal end of the instrument carrier the distal end thereof moves forwards. If the stem tube is bent downwards at its distal end, then the bending radius of the instrument carrier is greater than that of the optical unit, resulting in a shortening of the instrument carrier, so that with the fixed proximal end of the instrument carrier the distal end thereof is drawn with the electrode in the proximal direction.
With the bending direction last described above there is an electrical safety problem. If the electrode is greatly bent, the electrode can be retracted to such an extent that it touches the optical unit or comes too close to the optical unit. Since the optical unit does not usually have any special insulation provisions, when the electrode is supplied with high frequency current this can lead to a current flashover and, thus, to a current flow through the optical unit to the entire device. The consequences are burns to the patient and to the operator. This safety problem always occurs when the instrument carrier with the slider on which it is fixed is drawn in the proximal direction until the slider reaches a stop. Depending upon the design of the slider actuation means, this is the rest position of the slider or the slider may be drawn by the transporter out of the rest position and into the proximal stop position.
Therefore, there exists a need in the art for improved electrical safety for ureter resectoscopes.